Wall element for a protective device surrounding an operating or working area and protecting against laser beams from a laser source

ABSTRACT

The invention relates to a wall segment ( 10 ) for device, such as a cabin, a wall or a screen, protecting against laser beams from a laser source ( 38 ) and enclosing a work or effective zone, this wall segment comprising an inner wall ( 12 ) adjacent to the work or effective zone and an outer wall ( 14 ) parallel to the inner wall ( 12 ) and farther away from the work and effective zone than the inner wall ( 12 ). To activate an emergency OFF system to shut down the laser source or the processing machine, the inner and outer walls ( 12 ) and ( 14 ) resp. are metallic, for instance of iron or steel sheetmetal, the inner wall ( 12 ) being fitted at least on its side ( 18 ) facing the work or effective zone with a highly absorbent coating ( 16 ) and the side ( 22 ) of the outer wall ( 14 ) facing the inside wall ( 12 ) being of lower absorption.

DESCRIPTION

The invention relates to a wall segment of a protective deviceillustratively in the form of a cabin, a wall or a screen, enclosing awork zone or the effective region of laser beams from a laser source,said wall segment comprising an inner wall near the working or effectivezone and an outer wall parallel to the inner one and more remote thanlatter from this work or effective zone.

Such a protective device fitting a laser beam processing machine isalready known from the German patent document 89 08 806 U1. The wallsegments of this protective device consist of an outer glass or plasticpane, of a fusible wire as a conductor and meandering along the insideof the outer pane and of an inner pane of a plastic material or of oneabsorbing the laser beams. The fusible wire is connected by leads to anemergency OFF circuit of the processing machine. If during anomalousoperation of the processing machine the laser beam falls on one of thewall segments, the relatively high absorptivity of the material of theinner pane causes this pane to melt over a comparatively large area. Thegenerated temperatures are high enough to melt the nearest conductingwire and thereby to interrupt the low continuous current in it. Becausethe current is cut, the emergency OFF circuit, and hence the lasersource and the processing machine all are shut down. The emergency OFFcircuit is designed to respond before the glass pane of the wall segmenthas been fully melted by the incident laser beam.

Moreover surveillance techniques of fiber optics cables in the lasersystem or surveillance techniques of the laser optics are known. Whenlaser welding, the generated plasma also can be monitored using aphotocell. Lastly systems may be fitted into the laser optics whichbased on residual reflection detect whether beam from the laser sourcepasses through the optics and is scattered into the room.

The objective of all known surveillance or protective systems is toactuate an emergency OFF system allowing to shut off the laser source orthe processing machine.

Practical experience as well as past accidents have shown that suchknown surveillance systems do not provide 100% reliability against thelaser beam leaving the protective device because the emergency OFFdevice cannot in all conceivable cases be activated quickly enough toreliably preclude the laser beam from exiting the protective deviceuntil the above melting has been consummated.

Professional discussions also show that the known protective deviceshave been unsatisfactory. Illustratively requirements are set on thematerials used for the wall segments in the article “Abschirmungen anLaser-Arbeitsplaetzen” (“Screening laser work places”) in prEN 12,254 ofNovember 1995, however solutions were not offered. Furthermore the draftof the 20th IEC 8254 “Laserguards” has been discussed world-wide but ispresently being revised. This draft proposed passive wall segmentsfilled inside with pressurized water or air. These wall segments must beabsolutely tight, entailing high production costs.

Also, in case of malfunction, the water from the wall segment may escapeinto work sites or the likes, entailing electrical danger. If using suchpressurized containers as wall segments, further regulations relating topressurized-container safety may have to be observed. The above draftalso discussed active wall segments for a laser-beam protective system,with a design similar to that of the passive ones, but fitted withsensors detecting the inside pressure or the temperature differentialbetween the inside and outside spaces. While solutions of this kind maywell lead to satisfactory results, the design complexity and themanufacturing cost of such wall segments must be prohibitive.

On the other hand the objective of the present invention is to sofurther develop a wall segment of the initially cited kind that it willbe exceedingly simple to manufacture and that simultaneously it willmeet the present requirements of protective devices for the laserclass 1. Therein the wall segment must have a life of 100 seconds. Inother words, the laser beam may not pierce the wall segment within thistime interval. Furthermore the MZB values must be observed. Within thescope of the present application, the expressions “laser beams” or“laser sources” denote such lasers of which the powers are high enoughto be material-destructive. These laser sources may be CO₂, lasers withpowers up to 30 kw, further ecimer, helium, argon, ruby and Nd-YAGlasers.

Essentially the invention solves this problem by making the inner andouter walls of metal, for instance iron or steel sheetmetal, the innerwall being fitted at least on its side pointing toward the work oreffective zone with a highly absorbent coating and the absorptivity ofthe outer wall surface facing the inner wall being low.

This wall segment offers the advantage that in case of malfunction andof a diverging laser beam incident on the wall segment, the coatingdeposited on its side will be heated at the beam incidence and willstart to burn. The radial heat dissipation from the point of incidencebeing inadequate, the ignition site shall be narrowly constricted to acircular area provided suitable paints be used. The gases so generatedbroaden the beam beyond its own divergence, that is the beam is deformed(thermal blooming) and consequently the laser beam power density issubstantially reduced. The temperature near the edge of the divergingbeam is also substantially reduced by the gases generated in thecombustion of the inner wall coating. The outer wall side of lowerabsorptivity, ie of higher reflectance, reflects the heat energyradiated by the inner wall outer surface, and only slight heating of theouter wall side is to be expected during the 100 second interval. As awhole, the wall segment of the invention is exceedingly economical incost and design, the deliberate generation of gas or vapor at the siteof incidence caused by the errant laser beam creating effectiveattenuation of the laser beam by strongly scattering the laser light inthe gases or vapors.

In a first advantageous embodiment of the invention, the coating iscomposed of black paint. Because of the additional coating on the innerwall's inside, burning through the inner wall of the wall segment due toa malfunction will cause much gas or vapor to be formed between innerand outer walls of the wall segment and will assure further divergence,ie attenuation of the laser beam power density.

It was found advantageous in this respect to mount at least onepartition between the inner and outer walls. Such partitions areespecially useful when the wall segments are used to screen extremelyhigh power laser beams, for instance from Nd-YAG lasers operating atseveral kw.

The at least one partition may be made of metal, for instance iron orsteel sheetmetal and/or of graphite or graphite-coated sheetmetal.Graphite or graphite-coated sheetmetal is especially appropriate becauseof the high absorptivities involved. Illustratively special combinationsof partitions within the wall segment allow increasing the wall segmentlife beyond the value of 100 s, or else, screening laser beams of powersabove 10 kw.

In another advantageous embodiment of the invention, one partition maybe fitted at least on one side with a coating, especially of blackpaint. If in case of malfunction the inner wall should already have beenmelted by the laser beam, then the deposited coating on the partitionwill burn and generate gas or vapor, further broadening the laser beamwhich thereby is attenuated.

Further it was found advantageous to coat the partition adjacent to theouter wall with a highly absorbent paint and to make the partitionadjacent of the inner wall only slightly absorbent. This specialconfiguration further increases the life of the wall segment, or therequired strength also can be achieved at higher laser powers.

In many applications a partition consisting of a sheetmetal coated withgraphite or being all graphite was found practical.

The spacing between the wall segment's inner and outer walls isapproximately the diameter of the initial laser beam. The expression“initial beam” denotes the beam issuing from the laser before it entersthe optics. When observing this dimension, especially effectivescattering of the beam, that is attenuation of the power density, willbe achieved.

It was found advantageous that the spacings between adjacent walls, forinstance between inner wall and partition or between partition andpartition or between partition and outer wall, also approximatelycorrespond to the laser beam's initial diameter. It speaks for itselfthat larger spacings between walls may be used, requiring of coursefinding a tradeoff between maximum thickness of the wall segment and itseffectiveness.

Practical experimentation has shown that a spacing or 60 mm or morebetween adjacent walls is appropriate.

In a further advantageous embodiment of the invention the distancebetween the wall segment and the laser source shall be at leastfour-fold to five-fold the focal length of the laser optics. Inprinciple the wall segment may not be placed in the focusing range ofthe laser optics because of the very high power density present therein.Moreover such a configuration of the wall segments also takes intoaccount corresponding safety, that is accident regulations.

In another embodiment of the invention, the end faces of the multi-shellwall segment are preferably sealed on all sides. Thereby the wallsegments are easily handled and easily combined into a larger composite,and in addition the gases or vapors generated inside the wall segment incase of malfunction will be concentrated and prevented from escapingquickly.

In a further embodiment of the invention the wall segment comprisesboreholes in a vertical, upper segment, preferably in the zone of theend face. These boreholes allow constrained exhaust of the smokegenerated inside the wall segment during malfunction.

A smoke or gas sensor connected to a control unit and mounted betweenthe wall segment's inner and outer walls offers additional safety. Thiscontrol unit may emit emergency signals during malfunction and isparticularly appropriate for fully automated laser systems not alwaysattended by operators. However the control unit also may be used tocorrespondingly act on the laser, for instance by shutting it off or byreducing its power or the like.

In a further advantageous development of the invention, at least twosensors are mounted in the wall segment at different positions. The useof a second sensor takes into account the possibility of a laser beamhappening to be precisely incident during malfunction on one suchsensor, and accordingly the other one provides a useful redundantsystem.

In a particularly advantageous embodiment of the invention, the innerand outer walls and any partition(s) in between are fitted with mutuallyflush panes consisting of sequential polycarbonate or glass layers toallow optically monitoring the work zone from the outside and throughthe wall segment. It was ascertained that such pane configurationswithstand loading by CO₂ and also Nd-YAG lasers. Manifestly this featuremust be ascribed to the laser beam already losing significant power whenpassing through the first pane and therefore the load on the second andspaced pane is delayed. The time delay(s) can be further increased bymounting further pane(s).

As regards a protective device against laser beams fitted with at leastone wall segment, this device advantageously is a framework for ease ofmanufacture, this frame consisting of steel beams and the walls beingaffixed to it.

The invention is elucidated below in relation to the embodiments shownin the drawings.

FIG. 1 shows a first embodiment of the wall segment of the inventioncomprising one inner and one outer wall,

FIG. 2 shows a second embodiment of the invention of FIG. 1 comprisingan additional partition,

FIG. 3 shows a further embodiment of the wall segment of the inventionof FIG. 1, comprising two partitions,

FIG. 4 shows a further embodiment of the wall segment of the inventionof FIG. 1 comprising two partitions, one partition being made ofgraphite or being coated with it, and

FIG. 5 shows a further embodiment of the wall segment of the inventionof FIG. 1, with smoke sensors mounted in the inside space.

The wall segment 10 shown in FIG. 1 is part of a protective deviceagainst the beams of a laser source 38 and comprises at least an innerwall 12 and a substantially parallel outer wall 14. The inner wall 12and the outer wall 14 are metallic, preferably sheetmetal of iron orsteel, the inner wall 12 being fitted at least on its side 18 facing theregion subject to laser action, and preferably also on its outer side20, with a coating 16. Preferably the coating 16 is a paint of highabsorptivity, for instance black paint or the like. The side 22 of theouter wall 14 facing the inner wall 12 is only slightly absorbent. Thislow absorptivity or high reflectivity of the side 22 of the outer wall14 is attained in practice by merely using a substantially untreatedsheetmetal of iron or steel already comprising a reflecting surface andused as the outer wall 14. Clearly the side 22 of the outer wall 14facing the inner wall 12 may be subjected to special treatment orprocessing to increase reflectivity. Preferably the side 20 of the innerwall 12 shall also be coated.

In the embodiment of FIG. 2, a partition 24 uncoated on both sides ispresent in the gap between the inner wall 12 and the outer wall 14 andoffers low absorptivity, ie high reflectivity. It is understood that thepartition also may be coated on one or both sides with a highlyabsorbent coating of paint. Such different designs depend on theparticular applications.

In the embodiment of FIG. 3, two partitions 24, 26 are used, thepartition 24 being uncoated, ie reflecting, and the partition 26 beingcoated, ie absorbent, in a special embodiment mode.

In the embodiment of FIG. 4, again two partitions 24, 28 are presentbetween the inner wall 12 and the outer wall 14 of the wall segment, inthis case the partition 28 consisting of graphite or being agraphite-coated sheetmetal. The partition 24 on the other hand isuncoated and highly reflective.

It is understood that changes in the above embodiments matching theparticular applications can be used in the invention in arbitrarycombinations. The basic concept of the invention is to generateparticular gases, vapors or smoke, in the event of malfunction, byappropriately designing the wall segment 10. Individual walls fittedwith a coating 16 are provided for that purpose. Illustratively thepartition 26 may be fitted with a paint coat 30 at least on its inside32 or also additionally on its outside. The spacings 32, 34 between theparticular walls/partitions 12, 14, 24, 26, 28 substantially correspondto the diameter of the initial beam from the laser source 38. A space 34or 36 between adjacent walls/partitions 12, 14, 24, 26, 28 of about 60mm or more, was found practically appropriate. The distance 40 betweenthe wall segment 10 and the laser source 38 should be about four-fold tofive-fold the focal length of the laser optics.

The end faces 42, 44 of the multi-shell wall segment 10 preferably aresubstantially closed on all sides. However, as schematically andillustratively shown in FIG. 4, boreholes 50 may be present, preferablyin a vertical, upper segment, preferably in the vicinity of the end face42. Illustratively the construction of the wall segment 10 is aframework, the frame consisting of steel beams or similarcross-sectionally contoured beams, and the walls/partitions 14, 16, 24,26, 28 being affixed to the frame.

Preferably two smoke or gas sensors 46, 48 connected to a control unitare mounted in the gap between the inner wall 12 and the outer wall 14of the wall component 10 of the illustrative embodiment of FIG. 5.

PARTS LIST

10 wall segment

12 inner wall

14 outer wall

16 coating

18 side

20 side

22 side

24 partition (glossy)

26 partition (black)

28 partition (graphite)

30 coating of paint

32 side

34 spacing

36 spacing

38 laser source

40 distance

42 end face

44 end face

46 sensor

48 sensor

50 boreholes

What is claimed is:
 1. A wall segment (10) for a device enclosing a workzone to protect against laser beams of a laser source (38), the wallsegment (10) comprising an inner wall (12) adjacent to the work zone andan outer wall (14) substantially parallel to the inner wall (12) andfurther away from the work zone than the inner wall (12), characterizedin that the inner wall (12) and the outer wall (14) are both metallicsheet metal, the inner wall (12) is provided with a coating (16) atleast on a side surface of the inner wall (12) facing the work zone, anda side surface of the outer wall (14) facing the inner wall (12) beingof lesser absorption capability with respect to laser radiation than thecoating (16).
 2. The wall segment as claimed in claim 1, characterizedin that the coating (16) is black paint.
 3. The wall segment as claimedclaim 1, characterized in that at least one partition (24, 28) ismounted between the inner wall (12) and the outer wall (14).
 4. The wallsegment as claimed in claim 1, characterized in that the at least onepartition (28) is made of metal.
 5. Wall segment as claimed in claim 4,characterized in that one partition (26) is fitted at least on one ofits sides (32) with a coating (18).
 6. Wall segment as claimed in claim5, characterized in that the partition (26) adjacent to the outer wall(14) is fitted with a highly absorbent coating of paint (30) and thatthe absorption of the partition (24) adjacent to the inner wall (12) islow.
 7. A wall segment (10) for a device enclosing a work zone toprotect against laser beams of a laser source (38), the wall segment(10) comprising an inner wall (12) adjacent to the work zone and anouter wall (14) substantially parallel to the inner wall (12) andfurther away from the work zone than the inner wall (12), characterizedin that the inner wall (12) and the outer wall (14) are both metallicsheet metal, the inner wall (12) is provided with a coating (16)provided to absorb laser radiation at least on a side surface of theinner wall (12) facing the work zone, and a side surface of the outerwall (14) facing the inner wall (12) being of lesser absorptioncapability with respect to laser radiation than the coating (16);wherein at least one partition (24, 28) is made of one of iron sheetmetal and graphite-coated sheet metal; one partition (26) is fitted atleast on one of its sides (32) with a black-paint coating (18); and thepartition (26) adjacent to the outer wall (14) is fitted with a coatingof paint (30) provided to a absorb laser radiation so that the coating(16) on incidence of a laser beam begins to burn and that the absorptionof the partition (24) adjacent to the inner wall (12) is being of lesserabsorption capability with respect to the laser radiation than thecoating of paint (30).
 8. The wall segment as claimed in claim 1,characterized in that a spacing (34) between the inner wall (12) and theouter wall (14) corresponds approximately to the diameter of an initialbeam of the laser source (38).
 9. Wall segment as claimed in claim 1,characterized in that the spacings (36) between adjacent walls and/orpartitions such as between the inner wall (12) and the partition (24) orbetween the partition (24) and the partition (26, 28) or between thepartition (24, 26, 28) and the outer wall (14) corresponds approximatelyto the diameter of the initial beam of the laser source (38).
 10. Wallsegment as claimed in claim 1, characterized in that the spacing (34,36) of adjacent walls and/or partitions (12, 14, 24, 26, 28) is at least60 mm.
 11. Wall segment as claimed in claim 1, characterized in that thedistance (40) between the wall segment (10) and the laser source (38) isat least four-fold to five-fold the focal length of the fiber optics.12. Wall segment as claimed in claim 1, characterized in that the endfaces (42, 44) of the multi-shell wall component (10) are closed. 13.Wall segment as claimed in claim 12, characterized in that the boreholes(50) are present in a vertical, upper zone, in the zone of the end face942).
 14. Wall segment as claimed in claim 1, characterized in that asmoke or gas sensor (46, 48) connected to a control is mounted betweenthe inner wall (12) and the outer wall (14).
 15. Wall segment as claimedin claim 14, characterized in that at least two sensors (46, 48) aremounted at different positions in the wall component (10).
 16. Wallsegment as claimed in claim 1, characterized in that the inner and outerwalls (12) and (14) resp. and any partition(s) (24, 26, 28) mountedin-between comprise essentially mutually flush polycarbonate or glasspanes.
 17. Wall segment as claimed in claim 16, characterized in thatthe panes consist of at least two, more sequentially mounted layers. 18.A protective device against laser beams with at least one wall segmentas claimed in claim 1, characterized in that the protective device is aframework consisting of steel beams and that the walls and/or partitions(14, 16, 24, 26, 28) are affixed to this framework.
 19. The wall segmentas claimed in claim 1, wherein said inner wall and outer walls are madeof one of iron and steel.
 20. The wall segment as claimed in claim 4,wherein the at least one partition (24, 28) is made of one of iron sheetmetal, a steel sheet metal, and a graphite-coated sheet metal.
 21. Thewall segment as claimed in claim 5, wherein said coating (18) is ablack-paint coating (30).
 22. A laser beam protective device comprising:a first outer wall having a first surface facing towards a laser source,said first surface having a first coating of a material of relativelylow absorptivity and high reflectivity; and a second inner wall disposedbetween said first outer wall and said laser source, said second innerwall having an inner side facing said laser source and having a secondcoating of material of relatively high absorptivity; wherein said secondcoating burns when exposed to said laser beam.
 23. The laser protectivedevice according to claim 22, wherein said first outer and said secondinner wall are made of a metallic material.
 24. The laser protectivedevice according to claim 22, further comprising: at least one gassensor disposed between said inner and outer walls to detect gas emittedwhen said second coating of said second inner wall burns from exposureto said laser beam.
 25. The wall segment as claimed in claim 1,characterized in that the coating (16) is provided to absorb a laserradiation so that the coating (16) on incidence of a laser beam beginsto burn and the side surface of the outer wall (14) facing the innerwall (12) being of lesser absorption capability with respect to thelaser radiation than the coating (16).
 26. A wall segment (10) for adevice enclosing a work zone to protect against laser beams of a lasersource (38), the wall segment (10) comprising an inner wall (12)adjacent to the work zone and an outer wall (14) substantially parallelto the inner wall (12) and further away from the work zone than theinner wall (12), characterized in that the inner wall (12) and the outerwall (14) are both metallic sheet metal, the inner wall (12) is providedwith a coating (16) of black paint at least on a side surface of theinner wall (12) facing the work zone, and a side surface of the outerwall (14) facing the inner wall (12) being of lesser absorptioncapability than the coating (16).
 27. The wall segment as claimed inclaim 26, characterized in that the coating (16) is provided to absorb alaser radiation so that the coating (16) on incidence of a laser beambegins to burn and the side surface of the outer wall (14) facing theinner wall (12) being of lesser absorption capability with respect tothe laser radiation than the coating (16).
 28. The wall segment asclaimed in claim 1, wherein the coating has a high absorption capabilityof such kind that the coating on incidence of the laser beam begins toburn.
 29. The wall segment as claimed in claim 25, wherein the coating(16) is black paint.